Many photographers go to extreme lengths, such as waking up early in the morning, in an attempt to photograph public locations without having people walk through their photo. Historically, some photographers (with a lot of time on their hands) have utilized very dark neutral density filters over their lens, allowing very long exposure times in the hope that people in the way of their desired subject will keep moving, and their contribution to the resulting photo will be so blurred as to be undetectable. Other photographers have used large numbers of multiple exposures as people move around in front of their subject in the hope that each person will be in only one of the multiple exposures and their “ghostly” representation in the final image will be so faint as to be undetectable. These processes have worked well in certain situations, however, problems remain. First of all these exposures take a very long time to capture and extreme care must be taken in calculating exposure times. Secondly, even though the unwanted people are blurred or faint, there is still contribution to the final exposure by these unwanted subjects.